The filoviruses, Ebola (EBOV) and Marburg (MARV), cause periodic devastating hemorrhagic fever outbreaks in Africa. Because of the high rates of mortality caused by these infections and high transmissibility of these viruses in the human population, this group of viruses has been placed on the Category A select agent list that has been established by the Centers for Disease Control and Prevention. No anti-viral therapies are currently available against these deadly viruses. While recent developments of filoviral vaccines look promising, immunity to any vaccine is not immediate. One of vaccine candidates was recently shown to be somewhat effective when given 24 hours following lethal challenge suggesting that post exposure prophylaxis is possible. Furthermore, this study demonstrated that reduction in virus load during the infection had a significant impact on deleterious outcomes. These findings re-enforce the idea that antivirals that even transiently reduce virus load may be quite effective at decreasing mortality resulting from filovirus infection. The use of antivirals against filoviruses as a stop-gap measure against sporadic outbreaks will be highly beneficial even if vaccine development is successful as it is unrealistic to believe that wide spread vaccination of African populations against these viruses will occur in the near future. Here, we propose to develop such anti-viral therapy by the selection of nucleic acid aptamers against the receptor binding domain (RBD) of the EBOV surface glycoprotein GP1. Aptamers are oligonucleotides (generally 20-50 bp) that specifically bind to proteins or small target molecules. Aptamers can be selected that bind to a precise region of a protein and disrupt function. The EBOV glycoprotein GP1 RBD will serve as an excellent target for aptamers because this region of the protein resides extracellularly on both virions and infected cells allowing aptamers ready access to the molecule. Furthermore, aptamer interference of GP1 binding to its receptor(s) on permissive cells would effectively interrupt the viral life cycle and thereby reduce viremia within an infected individual and reduce spread of the virus to others. In Aim 1, we will select aptamers that target the GP1 receptor binding domain (RBD) and prevent binding of GP1 to permissive cells. In Aim 2, we will optimize the GP1 aptamer(s) and characterize aptamer stability and target affinity. We will then test the efficacy of the aptamers in blocking EBOV GP dependent transduction in cell lines and primary target cells. Development of aptamers that target EBOV GP and block virion entry into cells should prove highly successful in reducing viremia in the infected individual. Studies to date suggest that reduced viremia will not only prove effective at increasing survival of the infected individual, but will potentially reduce viral spread in a population and provide a means to transiently control outbreaks. PUBLIC HEALTH RELEVANCE: Outbreaks of the filoviruses, Ebola virus and Marburg virus, are sporadic and unpredictable. These viruses are frequently deadly and no current anti-viral treatments are available. Because of the lethality of these viruses and their ability to be rapidly transmitted within a human population, the filoviruses have been placed on the biodefense Category A list making antiviral development a top priority for scientists. Here, we propose to select small, synthetic RNAs called aptamers against the Ebola virus glycoprotein. Binding of the aptamers to the glycoprotein will block infection of the virus. Such novel antivirals could be used to control and limit the spread of the virus once an outbreak is detected.